Polyphosphazene-derived P/S/N-doping and carbon-coating of yolk-shelled CoMoO4 nanospheres towards enhanced pseudocapacitive lithium storage.

Transition metal oxides as potentialanodes of lithium-ion batteries (LIBs) possess high theoretical capacity but suffer from large volume expansion and poor conductivity. To overcome these drawbacks, we designed and fabricated polyphosphazene-coated yolk-shelled CoMoO4 nanospheres, in which polyphosphazene with abundant C/P/S/N species was readily converted into carbon shells and provided P/S/N dopants. This resulted in the formation of P/S/N co-doped carbon-coated yolk-shelled CoMoO4 nanospheres (PSN-C@CoMoO4). The PSN-C@CoMoO4 electrode exhibits superior cycle stability of 439.2 mA h g-1at 1000 mA g-1after 500 cycles and rate capability of 470.1 mA h g-1at 2000 mA g-1. The electrochemical and structural analyses reveal that PSN-C@CoMoO4 with yolk-shell structure, coated with carbon and doped with heteroatom not only greatly enhances the charge transfer rate and reaction kinetics, but also efficiently buffers the volume variation upon lithiation/delithiation cycling. Importantly, the use of polyphosphazene as coating/doping agent can be a general strategy for developing advanced electrode materials.